Piston pump



Oct. 18, 1960 G. A. WAHLMARK PISTON PUMP 3 Sheets-Sheet 1 Filed Sept. 29. 1958 Oct. 18, 1960 G. A. WAHLMARK 2,956,508

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PISTON PUlVIP Gunnar A. Wahlmark, Rockford, Ill., assignor to Borg- Warner Corporation, Chicago, lll., a corporation of Illinois Filed Sept. 29, 1958, Ser. No. 764,166

7 Claims. (Cl. 10S-162) The present invention relates in general to piston pumps and is more particularly concerned with piston pumps of the type having a rotatable cylinder block formed with a plurality of cylinders therein for respectively mounting a corresponding number of reciprocable pistons.

In piston pumps of the above mentioned general type to which the present invention is particularly pertinent, suitable means are ordinarily provided for pivotally mounting the rotatable cylinder block and rather complicated structure is therefore necessary in order to convey the pressurized uid from the cylinders, as it is expelled therefrom by the reciprocating pistons therein, to a fluid outlet which is `disposed in alignment with the pivotal mounting for the cylinder block mounting means. Obviously, this involves a rather complicated structure and is necessary in the event that it is desired that the piston pump be of the variable delivery type, wherein means must be employed for varying the angular disposition of the rotatable cylinder block, and the consequent throw of the pistons, within the pump casing.

The present invention comprises an improvement over conventional piston pump structures by providing means for conveying the pressurized iiuid from the pump cylinders directly to a uid outlet without the necessity of forming fluid passages in the cylinder block mounting means leading back to the point of pivotal connection between the cylinder block mounting means and the pump casing.

More particularly, it is an object of the present invention to provide a pump outlet comprising a pair of telescopically disposed sleeve members which are provided with a slidable seal disposed between the members and which are eective to accommodate relative sliding and angular movements between the members that become necessary to compensate for all of the different pivotal positions to which the cylinder block is movable Within the casing.

A still more detailed object of the present invention is to provide a fluid pressure outlet for a variable delivery piston type pump wherein the outlet includes a pair of telescopically disposed sleeve members for operatively interconnecting a pump valve control means with the casing outlet wherein one of the sleeve members is directly fixed to and in communication with the casing outlet, the other of the sleeve members has a ball and socket type connection with the pump cylinder mounting means, the inner of the sleeve members is formed with an annular groove around the outer periphery thereof with a substantially spherically shaped sealing ring disposed in said annular groove for engaging the inner periphery of the outer sleeve member to accommodate the relative sliding and angular movements between the sleeve members in order to compensate for all of the necessary pivotal positions of the cylinder block within the casing to enable variable delivery of the pump from a maximum to a minimum.

The foregoing objects and numerous advantages will become apparent from the following detailed description mice of the present invention when read in conjunction with the accompanying drawings wherein:

Fig. l is a side elevational view, shown partly in section, illustrating the principal features of the invention;

Fig. 2 is a sectional view illustrating certain features of the invention and taken substantially along the line 2-2 in Fig. l;

Fig. 3 is a sectional View further illustrating certain features of the invention and taken substantially along the line 3-3 in Fig. l;

Fig. 4 is an enlarged fragmentary view illustrating the cooperable sleeve members which together form the uid pressure outlet for the pump; and

Fig. 5 is an enlarged fragmentary view illustrating other features of the invention.

With reference now to the drawings, wherein like reference numerals have been used in :the different views to identify identical parts, the pump disclosed herein comprises a casing 10 formed with an annular opening 11 at one end thereof, which annular opening 11 is substantially closed by means of an end plate 11'2 which is secu-red to the casing 10 by means of a plurality of bolts 13 extending through suitable openings in the end plate 12 into threaded openings 14 formed in the casing 10. The end plate 12 is disposed in substantially sealed relation to the casing 10 by means of a suitable sealing ring 15 which lies within an annular groove 16 fo-rmed around the outer periphery of end plate 12 when the latter is in place in the end opening 11 of casing 10.

The casing 1li is also formed with a threaded outlet opening 17 within which a suitable bushing member 18 is received. A sealing ring 19 seals the bushing 18 with respect to the threaded opening 17 in casing 10. The lower end of bushing 18 forms a fluid pressure outlet sleeve member 20 which is rigidly disposed in place within the opening 17 in casing 10.

Substantially rigidly mounted Within the casing 10 is an annular drive shaft mounting member 21 which is securely held with respect to the end plate 12 by means of a plurality of bolts 22 which extend through suitable openings in a flange 23 on annular member 21 and are threaded into suitable openings 24 in end plate 12. The inner periphery of :annular mounting member 21 forms a series of races for several sets of roller bearings 25 and 26 and for a set of ball bearings 27. The bearings 25, 26 and 27 function to rotatably mount a pump driv ing member 28 disposed within the annular member 21 and in concentric alignment therewith. The pump driving member 28 is internally splined, as indicated at 29, for the reception of a drive shaft 30. A bushing 31 disposed in an axially Iextending ange portion 32 of end plate 12 is sealed with respect to the flange portion 32 by means of a sealing ring 33 extending therearound in an annular groove 34 and the seal ring 31 is formed with a substantially optically flat surface 35 with which a complementary substantially optically flat surface 36 formed on the end of a seal ring 37 cooperates in order to provide a seal between the interior of casing 10 and the interior of annular member 28. The seal 35-36 is an optical flat type seal and is held with its engaging surfaces together by means of a plurality of compression springs 38 disposed respectively in a plurality of axially extending openings 39 and in abutment with a stop ring 40 carried by means of annular member 28. A peripheral groove 41 formed around annular member 28 receives a sealing ring 42 therein, the outer periphery of sealing ring 42 being substantially spherical in shape in order to compensate for any slight misalignment between the seal member 37 and sealing ring 31.v

The ball bearings 27 are held in place, and serve 'as thrust bearings for the annular member 28, by means of the radially outwardly extending ange portion 43 of member 21 and the radially outwardly extending portion 44 of member 28. Roller bearings 25 and 26 are held against axial movement by means of suitableperipheral grooves formed around .the outer periphery of member 28 and a pair of spacer rings 45 and 46 are disposed between the roller bearings, 25 and 26.

' The annular member 21 is formed with a pair of op,- posed outwardly extending projecting portions 47 and 48 (see Fig. 3) and these projecting portions 47 and 4S pivotally mount a pair of cylinder block mounting members 49 and 50 by means of ball bearing assemblies 51 and 52. The cylinder block mounting members 49 and 50, which are pivotally mounted on the projections 47 and 48, are formed with inwardly extending end projections 53 and 54 against which complementary projections 55 and 56 of a fluid conducting block member 57 abut. The block member 57 and the mounting members 49 and 50 may be retained in integral relation by any well-known means, such as bolts. l

The block member 57 is formed with a substantially at Valve plate portion 58 against which a cylinder block 59 abuts. The cylinder block 59 is -formed with a concentric central opening 6ft therethrough and is rotatably mounted by means of a ball bearing assembly 61 havin-g, as its inner race, an extension 62 formed on a shaft member 65 which is positioned relative to the mounting block 57 by means of a Washer 64 which is disposed around the projecting shaft member 65. The shaft member 65 is retained within the block member 57 by means of a bolt 66 extending through the block member 57 and threaded into the end of shaft member 65. The shaft member 65 is hollow, as indicated at 67, and a hole 68 in the shaft member 65 communicates with a port 69 which is in communication with fluid in an inlet passage 70 in mounting block 57.

An annular member 71 is formed with a peripheral flange portion disposed within an `annular groove 72 formed around the inner periphery of cylinder block 9 and the annular member 71 is formed with a spherically shaped end portion 73 against which a complementary member 74 is continually biased by means of a cornpression spring 75 disposed within a cylindrical opening 76 formed in a drive shaft 77 adapted for drivingly interconnecting annular driving member 28 and cylinder block 59. The drive shaft 77 is formed with a plurality of radially outwardly extending arms 7S and 79 at its opposed ends and driving rollers l8() and 81 respectively rotatably mounted about projections 73 and 79 are received within 'axial extending slots 82 and 83 respectively formed within the interior of the end of annular member 28 and the interior portion 60 of cylinder block 59. Upon rotation of member 28, drive shaft 77 is rotated and this, in turn, drives the cylinder block 59. The drive shaft 77 is disposed in abutment with a pivot member 84 which is seated in a socket 85.

Suitable means are provided for lubricating the relatively movable parts comprising the drive mechanism and such means include axial opening S6 formed in member 71, axial opening y87 formed in member 74 and opening 88 formed in the end of drive shaft 77. Thus, fluid from inlet 70 may be communicated to the interior of drive shaft 77 so that it will be available for lubricating the movable parts of the drive shaft linkage through the axial extending openings just described.

The cylinder block 59 is provided with a plurality of spaced cylinders 89 within which a like number of piston elements 90 are respectively reciprocable. Each of the piston elements 90 is formed with a spherical ring seal 91 so as :to minimize linkage around the piston within the cylinder 89. The opposite end of each of the pistons 90 is formed with a substantially spherical portion 92 which is respectively received Within a complementary spheri cally shaped opening 93 formed in driving .member 28. Each of the spherical ends 92 is formed with a shoulder 94 adapted to cooperate with a plate 95 securely fixed to the member 28 by means of a plurality of bolts 96. Thus, upon rotation of member 28 with the cylinder block 59 disposed at an angle, as shown in Fig. 1, the pistons are caused to reciprocate Within their respective cylinders 89 in order to provide the necessary pumping action.

It will be noted that each of the cylinders 89 is formed with an open end 97 and this open end 97 is adapted to respectively cooperate with a kidney-shaped inlet 98 and with a kidney-shaped outlet 99 formed in the mounting block 57 and respectively in communication with inlet 70 and outlet 100. Thus, las the cylinder block 59 rotates and the respective pistons 919 are caused to reciprocate within their cylinders 89, they are etective to suck liquid through kidney-shaped opening 98 from inlet 7i) during approximately one half of each revolution of the cyl- Vinder block and to pressurize the liquid drawn into the cylinders and force it out under pressure through the kidney-shaped outlet port 99 duri-ing the other half of each revolution of the cylinder block 59.

The pump disclosed herein is provided with resilient biasing means 101 which is effective to hold the mounting members 49 and 5t) in an angular position, as'shown in Fig. l, in order that the pistons 90 may be able to perform a pump-ing action upon rotation of the cylinder block 59. The biasing means 101 comprises a pin member 102 seated within a suitable notch 103 formed at the top of one of the members 49 and 50 and received with-in a cup-shaped member 104. The cup-shaped member 104 is provided with a peripheral ilange 105 against which a compression spring 166 abuts. The compression spring 1116 is received within the cup-shaped portion 107 of a threaded cup 108 which is suitably mounted within casing 11i. A seal 169 is disposed around the cup 108 in order to effect sealing between the cup 16S and the casing 10. Thus, there is a continual biasing force by means of the spring 166 tending to cause the cylinder bloc'k 59 to be held in the position shown in Fig. l wherein .the pistons 9i) are effective to suck rluid from `the inlet 70 during yapproximately one half of each revolution of the cylinder block and to pressurize this iluid and force it out into outlet 190 during approximately the other half revolution of the cylinder block.

In order that the pump disclosed herein will be a variable delivery pump, means are provided for varying .the angular position of the cylinder block 59, `and the consequent throw ofthe pistons 90 in accordance with the output pressure of the fluid being pumped. Such means will now be described.

A cylindrical cup member is mounted within casing 10, and held in xed position relative thereto by means of a valve block 116, the cylindrical cup member 115 being substantially sealed with respect to the valve block 116 land formed with an end opening 117 in communication with a conduit 118 formed in the valve block 116. A piston 119 provided with a spherical sealing ring 120 disposed around its outer periphery and seated within a suitable peripheral groove therearound is pivotally mounted at its other end on a pin 121 carried by a piston-like element 122 reciprocable within the outlet 100. The piston-like element 122 is sealedwith respect to the inner periphery of outlet 191) by means of a sealing ring 123 which extends around and is disposed within an annular groove 124 formed in the piston-like element 122. The piston-like element 122 is formed with a central projection 125 which is received within the end of a cup-shaped member 126, with a compression spring 127 being disposed within the cup-shaped member 126 for taking up any axial play between the piston-like element 122 and the cup-shaped member v126. The cup-shaped member 126 is formed with a projection 128 adapted to be received Within a slot 129 formed in the lower end of Ia pin member 130 which extendsy across the lowerend of a sleeve member 131. The sleeve member 131 is formed with a substantially spherical surface 132 that is complementary to and received within an internal surface 133 formed around the outlet 100 and the upper end thereof. The complementary spherical surfaces 132 and 133 form a joint similar t'o a ball and socket joint. When the spherical surface 132 is forced upwardly resiliently it is caused to substantially sealingly engage the internal surface 133 of block member 57.

The other end of sleeve member 131 is received within the lower end of sleeve 20 which forms a second telescopic member and a spherical ring type seal 135 is provided for effecting a seal between the sleeve members 131 and 20. The spherical ring type seal 135 comprises a spherically shaped split ring 136 which is disposed within a suitable peripheral slot 137 formed around the outer periphery of the upper end of sleeve member 131. The spherical ring seal 135 thus enables axial misalignment of the two sleeve members without leakage of uid therebetween.

The sleeve member 20 is sealingly received within an opening 138 in casing 10, there being a sealing ring 139 therearound for maintaining this seal. The sleeve member 20 is internally threaded, as at 140 for receiving the end of a suitable pipe or conduit.

The valve block 116 is suitably secured to the casing and is sealed with respect thereto by means of a seal ring 141 which extends around the opening within which the cylinder 115 is received. The valve block is drilled to provide two coaxial cylindrical portions 142 and 143. A sleeve member 144 is received within cylindrical portion 142 and is formed with a shoulder 145 adapted to abut a complementary shoulder 146 formed within the valve block 116. The sleeve 144 is also provided with a pair of annular grooves 147 and 148 within which a pair of sealing rings 149 and 150 are respectively disposed. A plurality of ports 151 are effective to establish fluid communication from the interior of sleeve 144 to an annul-ar groove 152 which communicates with duct 118. A valve piston 153 is reciprocable within the sleeve 144 and is adapted to just close the ports 151, when the valve piston 153 Iis `in the position shown in Fig. 1. The valve piston 153 has a stem 154 which extends to the right into cylindrical portion 143 and is received within a cupshaped portion 155 of an annular member 156. The an; nular member 156 is provided with an annular shoulder 157 against which a compression spring 158 abuts, the compression spring 158 abutting a shoulder 159 at its other end carried by an adjusting member 160. The adjusting member 160 is sealed with respect to the Vvalve block 116 by means of a sealing ring 161 and is held in place by means of threaded region 162. A suitable lock nut 163 is provided for locking the member 116 in its selected position. A suitable bleed conduit 164 is provided so as to avoid having a pressure lock or hydraulic lock within the cylindrical portion 143 behind the piston 153.

Outlet pressure is conveyed to the cylindrical portion 142 of valve block 116 by means of suitable conduits 165 and this outlet pressure is effective to bias the valve piston 153 to the right so as to partially uncover ports 151. Thus, metered outlet pressure is applied to piston 119 after it has iirst overcome the compression force of the spring 158. When the output pressure is suiiiciently great, it causes the piston 119 to move upwardly and the piston 119, in turn, causes piston-like element 122 to move upwardly and this moves cup-like member 126 upwardly so as to cause the sleeve member 131 to be telescoped Within sleeve member 20. Inasmuch as the mounting block member 57 is pivotally mounted, movement of the sleeve member 131 upwardly causes the mounting block member 57 to likewise move upwardly and this will tend to change the horizontal position of the lower end of sleeve member 131.l Thus, there is some pivotal movement of the upper end of sleeve member 131 with- 6 in sleeve member 20. The spherical ring seal 135 conpensates for such pivotal motion.

As the output pressure continually builds up, a greater and greater force is applied to piston 119 to tend to move the mounting block 57 and cylinder block 59 in opposition to the basing of spring 106. Thus, as the pressure increases, the flow from the cylinders 89 is decreased and the output of the pump is likewise decreased. By changing the setting of member 160` in the valve block 116 the effect of the outlet pressure on piston 119 can be varied as desired.

By the use of the telescoping sleeve members 131 and 20 with the spherical ring seal 135 therebetween which l permits the necessary pivotal movement between the members, the outlet pressurized fluid is withdrawn from the pumpwithout carrying the same lback to the pivotal mountingl for the mounting block 57. It is contemplated that numerous changes and modifications may be made in the present invention without departing from the spirit or scope thereof.

What is claimed is:

1. In a hydraulic apparatus including a rotatable cylinder block having a plurality of cylinders therein, a plurality of` pistons respectively reciprocable within said cylinders for thereby enabling fluid to be drawn into the cylinders during approximately one half of each revolution of the cylinder block and enabling the uid to be expelled from the cylinders during approximately the other half of each revolution of the cylinder block, control means cooperable with said cylinder block for connecting said cylinders with a iluid inlet during said one half revolution of the cylinder block and with a uid outlet during said other half revolution of the cylinder block, said cylinder block being angularly movable between a rst position corresponding to maximum piston throw and a second position corresponding to zero piston throw, said uid outlet including means for compensating for the different positions of said cylinder block, and said compensating means comprising a pair of telescopically disposed sleeve members with a slidable seal therebetween `for enabling relative sliding and angular movements between said sleeve members.

2. A hydraulic apparatus including a casing and a relatively rotatable cylinder block disposed within said casing, said cylinder block having a plurality of cylinders therein, a plurality of pistons respectively reciprocable within said cylinders thereby enabling fluid to be drawn into the cylinders during approximately one half of each revolution of the cylinder block and enabling the iluid to be expelled from the cylinders during approximately the other half of each revolution of the cylinder block, a fluid inlet in said casing, a fluid outlet in said casing, control means cooperable with said cylinder block for operably connecting said cylinders with said iluid inlet during said one half revolution of the cylinder block and with said fluid outlet during the other half revolution of the cylinder block, means mounting said cylinder block for pivotal movement within said casing for varying the capacity of the apparatus between a maximum when the cylinder block is in a iirst position corresponding to maximum piston throw and a minimum when the cylinder block is in a position corresponding to minimum or zeropiston throw, and means comprising a pair of telescopically disposed sleeve members for operatively interconnecting said control means and said lluid outlet, there being a slidable seal disposed between the sleeve members to accommodate relative sliding and angular movements therebetween in order to compensate for all pivotal positions of said cylinder block within said casing.

3. A hydraulic apparatus including a casing and a relatively rotatable cylinder block disposed within said casing, said cylinder block having a plurality of cylinders therein, a plurality of pistons respectively reciprocable within said cylinders thereby enabling fluid to be drawn into the cylinders during approximately one half of each reveladas of the cylnderrblock andaablns tht-Hide to be expelled from the'cylinders during approximately the other half of each revolutionrof the-"cylinder block, a duid inletin said casing, a iluid outlet in said casing, control means cooperable with saidcylinder block for operably connecting said cylinders with said uid inlet during said one halfrevolution of the cylinder block and with said Fluid outlet during the other half revolution of the cylinder block, means mounting lsaid cylinderV block for pivotal movement within said casing -for varying the capacity of the apparatus between a maximum when the cylinder block is in a iirst position corresponding to maximum piston throw and a minimum when( thecylinder block is in a second position corresponding to minimum or zero piston throw, and means comprising a pair of telescopically disposed sleeve members for operatively interconnecting said control means and said uid outlet, one of said sleeve members being xed and in direct Huid communication with said outlet, Vthevother of said sleeve members having a ballandsocket type connection with said cylinder block mountingimeans, there being a slidable seal disposed between the sleeve members to accommodate relative sliding and angularmovements therebetween in order to compensate for all pivotal positions of said cylinder block within said casing.

4. A hydraulic apparatus including a casing and a rotatable cylinder block disposed within said casing, said cylinder block having a plurality of cylinders therein, a plurality of pistons respectively reciprocable Within said cylinders thereby enabling liuid to be drawn into the cylinders during approximately one half of each revolution of the cylinder block and enabling the uid to be expelled from the cylinders during approximately the other half of each revolution of the cylinder block, afluid inlet in said casing, a uid outlet in said casing, controlmeans cooperable with said cylinder block for operatively oonnecting said cylinders with said iluid inlet during said one half revolution of the cylinder block 'and'with said liuid outlet during the other half of each revolution of the cylinder block, means mounting said cylinder block for pivotal movement within said casing for varying the capacity of the apparat-us between a maximum when the cylinder block is in a first position corresponding to maximum piston throw and a minimum when the cyl- .inder block is in a second position corresponding to minimum or zero piston throw, and means comprising a pair of telescopically disposed sleeve members for operatively interconnecting said control means and said fluid outlet, the inner of said sleeve members being formed with an annular groove on the outer periphery thereof, a sealing ring disposed in said groove and in sealing relationship therewith, said ring being formed with asubstantially spherical outer surface engageable slidably with the inner periphery of the outer sleeve member to accommodate relative sliding and angular movements between the members in order to compensate for all pivotal positions of said cylinder block within said cylinder casing.

5, A hydraulic apparatus including a casing', a relatively rotatable cylinder block disposed within said casing, said cylinder block having a plurality of cylinders therein, a plurality of pistons respectively reciprocable within said cylinders thereby enabling fluid to bedrawn into the cylinders duringT approximately one half of each revolution of the cylinder block and enabling the uid to be expelled from the cylinders during approximately the other half of each revolution of the cylinder block, a 'uid inlet in said casing, a iluid outlet in said casing, control means cooperable with said cylinder block for operably connecting said cylinders with said fluid inlet during said one half revolution of the cylinder block and with said iluid outlet during the other half revolution of the cylinder block, means mounting said cylinder block for pivotal movement within said casing for varying the capacity of the apparatus between a maximum when the cylinder blookis in a first position corresponding to mum piston throw and a minimum when the cylinder block is in a second position corresponding'l to minimum or zero piston throw, and means comprising a pair of telescopically disposed sleeve members for operably interconnecting said control means and said Huid outlet, one of said sleeve members being iixed and in direct'uid communication with said outlet, the other of said sleeve members having a ball and socket type connection with said cylinder block mounting means, the inner oi` said sleeve members being formed with an annular groove around the outer periphery thereof, a sealing ring disposed iu said groove and in sealing relationship there 'with and said ring being formed with a substantially spherical outer surface slidable within the inner periphery of the outer sleeve member to accomodate relative sliding and angular movement between the members in order to compensate for all pivotal positions of said cylinder block within said casing.

6. A hydraulic pump including a casing and a relatively rotatable cylinder block disposed within said casing, said cylinder block having a plurality of cylinders therein, a plurality of pistons respectively reciprocable within said cylinders for drawing fluid into the cylinders during approximately one half of each revolution of the cylinder block and for expelling fluid from the cylinders during approximately the other half of each revolution of the cylinder block, a fluid inlet in said casing, a fluid outlet in said casing, control means cooperable with said cylinder block for operatively connecting said cylinders" with said fluid inlet during said one half revolution of the cylinder block and with said iluid outlet during the other half revolution of the cylinder block, means mounting said cylinder block for pivotal movement within said casing for varying the capacity of the pump between a maximum when the cylinder block is in a rst position corresponding to maximum piston throw and a minimum when the cylinder block is in a second position corresponding to minimum or zero piston throw, means comprising a pair of telescopically disposed sleeve members for operatively interconnecting said control means and said fluid outlet, there being a slidable seal disposed between the sleeve members to accommodate relative sliding and angular movement therebetween, and means responsive to the outlet pressure of said pump for varying the position of said cylinder block and, in turn, the throw of said pistons in the cylinders inversely with variations in the pump outlet pressure, said slidable seal between said telescoping members being effective to compensate for all pivotal positions of said cylinder block within said casing.

7. A hydraulic pump including a casing and a relatively rotatable cylinder block disposed Within said ca sing, said cylinder block having a plurality of cylinders therein, a plurality of pistons respectively reciprocable within said cylinders for drawing fluid into the cylinders during approximately one half of Veach revolution of the cylinder block and for expelling iluid from the cylinders during approximately `the other half of each'revolution of the cylinder block, a iiuid inlet in said casing, a iiuid outlet in said casing, control means cooperable with said cylinder block for operably connecting'said cylinders to said uid inlet during`r said one half revolution of the cylinder block and to said iluid outlet during the other half revolution of the cylinder block, means mounting said cylinder blockl for pivotal movement within said Vcasing for varying the capacity of the pump between a maximum when the cylinder block is in a rst position corresponding to maximum piston throw and :a minimum when the cylinder block Vis in a second position lcorresponding to minimum or zero piston throw, means comprising a pair of ltelescopically disposed sleeve members for operatively interconnecting said control means and said fluid outlet, one of said sleeve members being in direct huid communication with said outlet?, the other of said sleeve members having a ball and socket type connection with said cylinder block mounting means, and a uid pressure responsive piston responsive to the outlet pressure of said pump for simultaneously retaining said ball and socket connection in substantially sealed engagement and varying the position of said cylinder block, and, in turn, the control of said pistons in the cylinders inversely With variations in the pump outlet pressure, said slidable seal between said telescoping members being effective to compensate for `all pivotal positions of said cylinder block Within said cas-ing.

References Cited in the le of this patent UNITED STATES PATENTS 

